This invention relates generally to the process of isotope exchange and in particular to the oxygen isotope exchange on an oxide-containing catalyst.
New approaches for extending the life of lasers used in space applications are under investigation. One aspect of the rapid progress in this area is that new techniques for long lifetime space applications of high pulse-energy, common and rare isotope, closed-cycle CO.sub.2 lasers are being studied. The high-energy pulsed CO.sub.2 laser must be operated closed-cycle to conserve gas, especially if rare isotope gases are used. Rare-isotope gases, such as C.sup.18 O.sub.2, are used for improved transmission of the laser beam in the atmosphere.
The electrons in electric-discharge CO.sub.2 lasers cause dissociation of some CO.sub.2 into O.sub.2 and CO and attach themselves to electronegative molecules such as O.sub.2, forming negative O.sub.2.sup.- ions, as well as larger negative ion clusters by collisions with CO or other molecules. For closed-cycle, sealed CO.sub.2 laser operation, the concentration of negative ions/clusters may become sufficiently high to form discharge instabilities which may ultimately disrupt the CO.sub.2 laser operation. The decrease in CO.sub.2 concentration due to dissociation into CO and O.sub.2 will reduce the average repetitively pulsed or continuous wave (CW) laser power, even if no disruptive negative ion instabilities occur. In order to maintain laser power, i.e., maintain CO.sub.2 concentration and reduce negative ion formation, the recombination rates of CO and O.sub.2 must be increased, or the dissociation reduced. In essence, there are two techniques to accomplish these goals. One involves modification of the CO.sub.2 :N.sub.2 :He laser mixture to increase the recombination and modification of the electric discharge behavior to reduce the dissociation. The other involves CO--O.sub.2 recombination, catalyzed by solid-state catalysts with sufficiently high recombination rates at temperatures which are not excessive and which may be attained by heating from the laser medium or other means of using the dissipative non-lasing power.
The catalysts which function well at such lower temperatures, generally obtain oxides which can participate somewhat in the recombination process. Participation is through oxidation of the dissociation product, CO, by the catalyst, and concurrent reoxidation of the catalyst oxide by the other dissociation product, O.sub.2. These two steps permit a reactive oxide catalyst to function as a true catalyst which maintains its structure during the catalytic recombination process. Thus, the interaction of the catalyst oxides with the dissociation products CO and O.sub.2 occurs, in part, through reaction of the oxygen in the catalyst with CO, forming CO.sub.2, and replenishment of the oxygen lost from the catalyst with the dissociation product O.sub.2. Recalling that laser operation using a rare isotope such as C.sup.18 O.sub.2 provides improved atmospheric transmission, it would therefore be desirable to provide a catalyst capable of catalyzing CO--O.sub.2 recombination involving a rare oxygen isotope without any introduction of common-isotope oxygen from the catalyst into the gas molecules.
The first technique, that is, modification of the CO.sub.2 :N.sub.2 :He laser mixture to increase recombination, involves additions of CO to the laser gas. However, the second technique is more advantageous in that solid catalysts can provide higher CO/O.sub.2 recombination rates than gas additions with resulting lower average power reduction and higher efficiency of closed-cycle, repetitively pulsed or CW lasers. Higher operating temperature (.gtoreq.200.degree. C.) catalysts such as Pt or Pd alone or on some non-interactive substrate, such as Al.sub.2 O.sub.3, have been frequently used to achieve high recombination rates. The purpose of substrates is to increase the catalyst surface area and offer support. However, the necessity for external heating to high temperatures reduces the total system efficiency for space based operation, and is also undesirable for other contemplated applications. To conserve energy, the catalyst must be active at or below 100.degree. C., the temperature inside the laser envelope. Neither technique currently known in the prior art will provide for such operation at long lifetimes.
Accordingly, it is an object of the present invention to develop a catalyst that will provide for the recombination process using a rare oxygen isotope such as .sup.18 O within a closed-cycle, CO.sub.2 laser without loss of isotopic integrity in the laser gas.
It is a further object of the present invention to develop a catalyst that will provide active recombination within the closed-cycle, CO.sub.2 laser without any additional heating of the catalyst.
A still further object of the present invention is to provide a catalyst that will provide for active recombination over a long period of time.